Aircraft: SMALL AIRCRAFT; LOW WING; 1 ENG; RETRACTABLE GEAR
Phase of flight: Final Approach
Anomaly: Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy

I was enroute to TCY with VFR Flight Following. When about 10 NM NNE of TCY; NORCAL (123.85) advised me of traffic ahead on approach to TCY Runway 12; and to squawk VFR and change to TCY advisory frequency (CTAF 123.075). TCY is an uncontrolled field with standard left hand patterns. TCY AWOS said wind was something like 300 deg at 15 knots gusting to 20; so I decided to land on Runway 30 and I announced my position on the CTAF. I can't remember whether ATC told me the type of traffic on approach to Runway 12 but I will refer to it as [Aircraft Y]; the #2 airplane in this report. [Aircraft Y] announced his position several times also and I saw him as we both passed over the Runway 12 threshold at about the same time. The pilot had an Asian accent (Japanese?) and I had trouble understanding him. [Aircraft Y] was quite low and I was several hundred feet above; descending rapidly for a left downwind to Runway 30. [Aircraft Y's] track was aligned with Runway 12. I would estimate my heading as 150 degrees; crossing to the west of [Aircraft Y's] track. I lost sight of [Aircraft Y] at this time and assumed he would execute a standard missed approach to the ECA VOR; which is what I have done when practicing Runway 12 instrument low approaches into TCY. That would have taken [Aircraft Y] away from the TCY airport headed to the NW; such that he would not be a factor for my left downwind pattern for Runway 30. While on left downwind I was surprised to hear an aircraft announce he was on right downwind for landing on TCY Runway 30 and wondered why someone would be flying a RH pattern. By the voice accent I realized it was the same [aircraft] but I didn't know his flight path and assumed I was ahead of him. I also assumed he would abandon his approach when he saw that I was in the standard left hand pattern and he was not. However both of my assumptions were wrong and we both turned base and final; and [Aircraft Y] climbed out while I landed. I'm guessing we got to less than 300 feet of one another and I could clearly see it was a low wing blue and white single engine aircraft. I lost sight of the [aircraft] while concentrating on the landing (gear down etc) and never heard from him again. I don't know whether he intended to land or just do a low approach to Runway 30. I was further primed to expect [Aircraft Y] to abandon the approach because a couple years earlier; on a VFR training approach on the MCC ILS with an instructor; when another aircraft announced he was landing in the opposite direction; which the wind favored; my instructor told me the landing aircraft had priority and to break off our approach. So I assumed that VFR practice approaches had lower priority at non-towered airports. I have since reviewed the FAR's and AIM wondering who had priority in this conflict. I see that the TCY Runway 12 approach has circling minimums and it would be a right hand pattern to Runway 30 because the approach plate says circling NA on the SW side of the airport (the left hand pattern). Aside from arguing who was ahead or lower altitude etc; it appears that we were both operating legally; one in a RH traffic pattern and the other in a LH traffic pattern.In hindsight I should have broken off my approach before we got so close to each other because we both contributed to creating a dangerous situation. Also on hindsight I think I may have heard [Aircraft Y] announce something about 'circling' but due to the accent (Asians have trouble with the 'L' sound) and my not being familiar with the TCY circling approach; I didn't anticipate the upcoming conflict.I don't know whether Norcal knew [Aircraft Y] was going to do a circling approach; he didn't mention it to me. I wonder whether non-instrument rated pilots would be expected to anticipate authorized traffic in a RH pattern at TCY.I also noticed that AG pilots have an exemption to standard patterns at non-towered airports but with the exception that they must at all times remain clear of; and give way to; aircraft conforming to the traffic pattern for the airport. FAR 137.45 (d). That would be a nice addition to Part 91 Operating Rules for aircraft on IFR approaches in VFR conditions at airports without functioning control towers. Reviewing the MCC ILS approach; I see that circling is NA; so maybe that is what my instructor had in mind for telling me to break off the practice ILS approach a couple of years ago. I haven't had a chance to talk with him about it yet. A pilot on a left downwind to the TCY Runway 30 had a near miss on final with an aircraft whose foreign accented pilot had just completed a practice instrument approach to Runway 12 and broke the approach off entering a Runway 30 right downwind to final.